1. Field of the Invention
This invention relates to instrumentation for achieving spinal fusion and, more particularly, to a spinal fixation apparatus and method for fixation of the lumbar spine and the lumbosacral spine to aid the fusion of these regions of the spine.
2. The Prior Art
The spine is a flexible, multisegmented column that serves to maintain the upright posture while providing mobility to the axial skeleton. The spine also protects the delicate neural structures of the spinal canal. In fulfilling these functions, the spine can be subjected to large forces. These large forces are assumed to play a dominant role in the etiology of low back pain. Excessive forces on the spine can also produce life-threatening traumatic injuries and may contribute to an increased rate of degenerative change.
The lumbar spine serves two basic functions. It encases and protects vital neural elements and provides structural support for the body by transmitting the weight of the body through the pelvis to the lower extremities. Since there are no ribs attached to it, the lumbar spine has a relatively wide range of motion.
The back is made up of bone, intervertebral discs, synovial joints with their articular cartilage, synovial capsules and supporting ligaments, muscle, fascia, blood vessels, nerves, and skin. As in other areas of the body, these elements are subject to a variety of pathological disturbances: inflammation, trauma, neoplasm, congenital anomalies, etc. Trauma frequently results in damage at the upper end of the lumbar spine, where the mobile lumbar segments join the less mobile dorsal spine. Degenerative changes tend to develop in the lower lumbar intervertebral discs, most commonly in the third decade. Osteoarthritis produces changes in the facet joints by middle age. Pain in the low back is a complaint of about 80% of the members of the human race at some period of life and is responsible for a large percentage of patient visits to physicians.
One of the methods used to treat disabling pain and neurological compromise produced by any of the above noted pathological conditions has been spinal fusion. Spinal fusion has been a controversial topic since the first procedures were performed in the early nineteen hundreds. Indications and techniques were argued then and continue to be a constant source of lively discussion in the orthopedic literature. It is also interesting to note that the development of spinal fusion techniques predates the understanding and surgical treatment of lumbar disc disease. It is the intersection and intermingling of indications for these two procedures, disc excision and lumbosacral fusion, that have produced the most controversy.
The earliest spinal fusion techniques were basically posterior interlaminar fusions. Subsequently, a few years of experience with these techniques led to the evolution of posterolateral techniques allowing a larger area for bone grafting and fusion. However, as orthopedists recognized the relatively high rate of unsatisfactory results with the traditional fusion techniques, they developed new ones. The continued evolution of lumbosacral fusion has involved the use of hardware or instrumentation in attempting to achieve either stability and thus fusion or correction of deformity and stability followed by fusion. When one considers the numbers of patients who have been treated surgically and followed for decades, it is amazing that it is still not possible to garner a strong scientific consensus on the efficacy of lumbosacral fusion from the literature. Various studies have been conducted over the past several decades and have determined that satisfactory results were obtained in 60% of the cases with disc excision alone and 70% satisfactory results in the fusion group. The conclusion was that despite the slightly better results in the fusion group, the morbidity risk from the fusion procedure meant that the indicated operation was disc excision alone with the recommendation that fusion be performed later if the patient failed with persistent symptoms secondary to instability or degenerative changes. Another study that looked into all aspects of instability whether in the vertical plane (narrowing, olisthesis), the horizontal plane (articular process disease), the frontal plane (scoliosis), and the sagittal plane (spondylolisthesis, compression fracture) concluded that only about one-third of these patients should be fused primarily. However, based upon my experience as an orthopedic surgeon, I have concluded that the ambiguous results from the earlier studies were the result of inadequate, cumbersome, and poorly designed instrumentation for achieving fixation in aid of lumbar fusion.
One can well ask, why use instrumentation in lumbosacral fusion. Fusion is performed in the unstable spinal segment that one wants immobile. Internal fixation increases rigidity and results in a high rate of fusion. This increased fusion rate and decreased pseudarthrosis rate give better results and can significantly reduce postoperative pain and time for convalescence. Spinal instrumentation also allows correction of deformity and maintenance of that correction during consolidation by fusion. Although there are no generally accepted answers to the question of what are the general indications for instrumentation, it is possible to propose a logical schema to guide the spinal surgeon in making these important decisions. The primary considerations are the magnitude of instability, the plane of deformity, and the available intact anatomy.
The past decade or two has seen an extensive development of internal fixation devices for the lumbar and lumbosacral spine. The most common rationale for using such devices is to reduce the incidence of pseudarthrosis after bone grafting. Another rationale (typically for trauma management) is to maintain intervertebral alignment to protect the neural elements until healing occurs. One of the early fixation methods was the placement of screws obliquely across each facet joint involved in the grafting. However, the pseudarthrosis rate was unacceptably high. Numerous other types of devices that variously include plates , wires, rods, bolts, hooks, and, of course screws, have evolved since that time and have resulted in a plethora of devices being available for use by the orthopedic surgeon. Although not provided by all these devices, the ideal device would provide internal alignment and fixation not just in any one of the various planes of movement but in a full, three-dimensional construct.
Numerous patents have been issued for various types of spine fixation devices. These devices employ different mechanical apparatus for enabling the surgeon to selectively adjust the alignment of the patient's spine and then to secure that alignment with the spine fixation device. Edwards (U.S. Pat. No. 4,569,338) discloses a sacral fixation screw having an opening through the head of the screw. A rod-mounted hook is mountable to the opening to interconnect the rod to the sacrum for spinal fixation purposes.
Steffee (U.S. Pat. Nos. 4,648,388 and 4,719,905 discloses a rod, a plurality of clamps, and a plurality of fastener assemblies. The clamps are fastened to selected vertebra and the clamps are tightened against the rod which has been selectively bent to conform to a preselected contour to hold the spine in the desired orientation.
Howland et al (U.S. Pat. No. 4,653,481) disclose a plurality of screw clamp assemblies that are inserted into the vertebral body through the pedicle and are used as anchors for rigid rods which have been selectively bent to conform to a preselected contour to hold the spine in the desired orientation.
Puno et al (U.S. Pat. No. 4,805,602) disclose a transpedicular screw and rod system for the internal fixation of the spine. The rod is held in position against the vertebral lamina by an anchor which is secured to the vertebrae by the transpedicular screw.
Sherman (U.S. Pat. No. 4,887,596) discloses an open backed pedicle screw for use in internal spinal fixation. The open back includes a yoke for receiving a rod and a clamping mechanism for clamping the rod against a cusp in the yoke while permitting angular adjustment between the rod and the yoke.
Gotzen et al (U.S. Pat. No. 4,944,743) disclose an implantable fixation device having a support bar having right-hand threads on one end and left-hand threads on the other end. Jaw supports are threadedly mounted on the respective threaded ends. Bolt jaws are secured to the jaw supports and affixed to intact vertebral bodies of the spinal column.
Gaines, Jr. (U.S. Pat. No. 4,950,269) discloses a spinal column fixation device for connecting vertebrae. The device includes a pedicle screw and a mounting system for mounting a rod to the head of the screw. A cap is engageable on the screw head and is used to retain the rod to the screw.
Krag et al (U.S. Pat. No. 4,987,892) disclose a spinal fixation device wherein at least two pedicle screws are interconnected by a rod. Clamps adjustably secure the rod to the pedicle screws.
Cotrel (U.S. Pat. No. 5,005,562) discloses a spinal fixation device including pedicle screws, and sublaminar hooks interconnected by rods. The pedicle screws and the sublaminar hooks are configured with an open, threaded yoke into which a set screw is threadedly inserted to secure the rod to the pedicle screw and the sublaminar hook.
However, my experience has shown that each of these prior art devices are either cumbersome to implant, difficult to adjust, or require undue surgical time in their implantation. Further, since there is such a wide variation in spinal dimensions and availability of suitable attachment sites, certain of these devices have only limited application. Another problem equally important is that of accurate placement of the pedicle screws followed by subsequent adjustment of the interconnecting rods, wires, hooks, etc., once the pedicle screws are in place.
In view of the foregoing, it would be a significant advancement in the art to provide a spinal fixation apparatus and method that is highly adaptable in its placement, easily adjustable after securement of the pedicle and/or sacral screws, and provides ample support or fixation in all planes. It would also be an advancement in the art to provide a spinal fixation apparatus and method wherein the pedicle screws are quickly and accurately placed for providing the optimal securement of the screws. Such a novel spinal fixation apparatus and method is disclosed and claimed herein.